Ringless piston

ABSTRACT

A ringless piston in which a sealing flange at one or both ends of the piston has a thickness such that it expands under working pressure and in accordance with bursting tendencies of the flange. The piston and flange in the absence of pressure within the cylinder have a normal running clearance with the cylinder wall.

United States Patent Costarella July 17, 1973 [54] RINGLESS PISTON3,150,570 9/1964 Johnson et al 92 172 x 3 .t 92 240 X [76] lnventor:Nino F. Costarella, 5311 S. Howell 266385 8/1966 Scdrdmucu 1 Avenue,Milwaukee. Wis. 53207 [22] FHed: June 9, 1971 Primary Examiner-Martin P.Schwudrun Assistant Examiner-A. Hershkovlltz PP NOJ [SL268Att0rney-Mann, Brown, McWilliams & Bradwuy Related US. Application Data[63] Cnntinuation-in-part of Ser. No. 800,956, Feb. 20,

1969, abandoned. [57] ABSTRACT [52] US. Cl 92/192, 92/243, 92/246 A i lpiston i which a scaling flange at one [5 l both ends of the iston has athickness uch thal ex. [58] Field of Search 92/l72, 240, 192, pandsunder working pressure and in accordance with 92/243, 246 burstingtendencies of the flange. The piston and flange in the absence ofpressure within the cylinder have a [56] References C'ted normal runningclearance with the: cylinder wall.

UNITED STATES PATENTS 3,132,569 5/1964 Shepherd 92 172 x 6 Claims, llDrawing Figures.

PAH-1mm JUL I 1191s saw 1 or 2 l ll jhverz 287 I JZZ'IZG F CESZQWe/ZQ/PAIENTED Jui I 7 3 SHEET 2 OF 2 RINGLESS PISTON This application is acontinuation-in-part of my copending application Ser. No. 800,956, filedFeb. 20, l969,"and now abandoned.

The present invention is directed to new and useful improvements inpiston and cylinder assemblies of the type used as pumps, engines andother apparatus wherein pressure is developed between the piston andopposed end wall of the cylinder during reciprocation of the piston.

For years it has been more or less customary to use piston rings ofvarious types on the outer walls of the pistons in pressure developingpiston and cylinder assemblies. In such cases the piston has a runningor working clearance with the opposed wall of the cylinder which may beon the order of one thousandth of an inch for every inch of pistondiameter. In such cases, separate piston rings are carried in grooves onthe outer periphery of the piston and are fitted so as to provide somesealing contact with the opposed wall of the cylinder duringreciprocation of the piston. In assemblies of this type, the rings wearout and must be replaced and the use of pistons of this typenecessitates assembly and machining time to provide the rings for thepiston. Various proposals have been made from time to time in the pastto form ringless pistons. In some of these cases, pistons are formedwith skirt-like flanges on one or both ends of the piston and pressureringsare inserted within the flanges to more or less bend the flangesoutwardly so that the extreme end of the flange makes more or less of aline contact with the wall of the cylinder. In other cases, proposalshave been made to eliminate the use of rings by forming the piston witha diameter which is at least as great as the inside diameter of thecylinder so as to provide a form of press fit between the piston andcylinder. For some reason or another, these proposals have not gone intowidespread use and the ring-type piston construction is still the mostwidely used construction as of the present time, possibly because of thewear that occurs when a line sealing contact is established by a pistonflange and because of the difficulty holding manufacturing tolerancessuch that a piston can be press-fitted within the cylinder and at thesame time provide an operable machine without large frictional losses orexcessive costs.

With the foregoing in mind, the primary purposes of the presentinvention are to create a ringless piston and cylinder constructionwhich, when manufactured, has the normal operating or running clearancesor tolerances between the piston and the cylinder and which, whensubjected to the normal operating pressure developed within the pistonand cylinder, causes an expansion of specially-formed wall surfaces ofthe piston outwardly into a sealing contact with the wall of thecylinder to provide a relatively large area of wall-to-wall contactwhile at the same time holding frictional losses developed duringreciprocation of the piston to a minimum.

These and other objects of the invention will become more apparent inthe course of the ensuing specification and claims when taken with theaccompanying drawings, in which:

FIG. I is a side elevation in section of a typical piston formed inaccordance with the principles of the present invention;

FIG. 2 is an enlarged detail view of a portion of the piston illustratedin FIG. 1;

FIG. 3 is a diagrammatic sectional view illustrating, in schematicfonn,the manner in which the piston of the present invention operates;

FIG. 4 is a schematic view of a piston formed in accordance with theinvention and illustrating wear marks on the piston;

FIG. 5 is a sectional illustration of a modified form of the invention;

FIG. 6 is a sectional view of another modification of the invention;

FIG. 7 is a sectional view of another modified form of the invention;

FIG. 8 is a sectional view of another modified form of the invention;

FIG. 9 is a sectional view of another modified form of the invention;

FIG. 10 is a sectional view of another modified form of the invention;and

FIG. 11 is a sectional view of another modified form of the invention.

Like elements are designated by like characters throughout thespecification and drawings.

With specific reference now to the drawings, and in the first instanceto FIG. 1, the numeral 10 generally represents a piston formed inaccordance with the present invention. The piston is mounted forreciprocation in a cylinder which is diagrammatically represented by thebroken lines 11 in FIG. 1. Cylinder 11 may take any one of a number ofknown forms. The piston and cylinder assembly thus defined may be usedin apump, an hydraulic or air cylinder, a shock absorber or accumulator.

The main portion 12 of the piston may, if used as a part of an hydraulicram assembly, be provided with a central opening 13 for reception of anoperating piston rod or ram in a manner known to the art. On the otherhand, the central opening 13 may be omitted and suitable facilities maybe provided with the main body portion 12 to enable connection to aconnecting rod. Since such piston actuating members and connections areknown to the art, and since they form no part of the present invention,they are not illustrated in the drawings.

In accordance with the invention, one or both ends of the piston body isformed with a generally cylindrical skirt-like flange 14. As illustratedin the drawings, a flange 14 is provided on opposite sides of the mainbody of the piston. In situations where only one side of the piston issubjected to pressure, only one flange need be provided, and on the sideopposed to the pressurized space within the cylinder.

As shown in FIG. 2, the skirtllike flange 14 has a length several timesits width. The length should be approximately equal to the pistonexternal diamete divided by four. The exterior diameter of theskirt-like flange or flanges I4 is machined or formed so as to be thesame as the exterior diameter of the main body portion of the piston.Both diameters are such as to provide a normal running clearance withthe opposed cylinder wall 1]. This clearance may be 0.001 inch for eachinch of piston diameter. The exterior surface of the flanges 14 maycarry relatively shallow oil entrapping grooves 15 which are spacedaxially of the piston. Shallow oil entrapping groove 15 may also beprovided medially of the piston. These oil entrapping grooves shouldhave depths considerably less than one-half of the radial width of theflanges and preferably no more than one-fifth of the overall wallthickness of the flange, when the overall wall thickness is 0.025 inchor less. When the wall thickness is 0.050 inch or more, the groove depthshould not exceed 0.010 inch.

It is within the concept of this invention to form pistons which do nothave oil entrapping grooves. Such a construction is illustrated in FIG.11. The piston and opposed skirt-like flanges are formed in accordancewith the criteria set forth herein. With double-acting cylinders, theaction of flanges on opposite sides of the piston naturally tends towork lubricant back and forth within the cylinder without use of oilentrapping grooves.

It is also within the concept of this invention to use an oil wipingring of Teflon or the like at one portion of the piston as, for example,in the medial groove 15. An O-ring of this type does not function as anormal piston ring but functions merely to confine flow and positioningof lubricating oil. In some cases this is particularly advantageous, asin the case of double-acting pistons of hydraulic cylinders when thepressurized condition is changed from one end of the cylinder to theother. As the changeover is being made, a ring of this type will tend toprevent oil blow-by before the pressurized flange is expanded.

The flanges 14 are formed so as to expand in more or less barrel-likefashion as illustrated in the exaggerated showing of FIG. 3. This isdone by proper selection of radial widths of the flanges. For example,the wall thickness of the flange at one end or both ends of the pistonmay be calculated for any' given piston and cylinder construction. Forexample, for a cylinder with a 4.250 inch bore and a reciprocable pistonwith a 4.245 inch outside diameter, a typical running clearance Cbetween the piston and cylinder wall of 0.005 inch exists. Thecross-sectional clearance area between such a piston and cylinder may becalculated as 0.03336 square inch. The pressure within the pressurizedspace of the cylinder may then be calculated or approximated. Forexample, if the pressure is supplied by an hydraulic pump supplying avolume of oil at 40 gallons per minute, the pressure in the pressurizedspace may be calculated by the formula: Gallons per minute 24.12 X theleakage area between the piston and cylinder in square inches X thesquare root of the final pressure in the pressurized space. With theassumed figures, the formula then becomes: 40 24.12 X 0.03336 X thesquare root of the final pressure.

From this, final pressure may be calculated as 247i p.s.i. in thepressurized space of the cylinder. The actual working pressure withinthe cylinder may be below this calculated pressure and a pressureconsiderably below the calculated and actual working pressure may thenbe utilized to determine a flange wall thickness which will cause theflange to expand and seal against the opposed wall of the cylinder. Forexample, a pressure of 800 p.s.i. may be assumed to be adequate forinsuring a sealing relation under the calculated pressure condition of247i p.s.i. The tensile strength of the piston material must be knownbefore the wall thickness can be calculated. The tensile strength ofmost, if not all, piston materials is readily available from engineeringhandbooks or data supplied by manufacturers of piston material. As aspecific example, if the piston material is made from SAE Class 30 castiron, the tensile strength of the material is 30,000 p.s.i.

Then Barlows formula for the burst pressure of a cylinder under internalpressure may be used to calculate the necessary wall thickness of theflange or flanges on the piston to insure sealing of the flange againstthe cylinder wall under the assumed pressure condition. Barlows formulais: pressure p.s.i. 2 X wall thickness in inches X the tensile strengthof the material divided by the diameter of the cylinder.

By substituting values then, 800 p.s.i. 2 X the wall thickness X 30,000(tensile strength) divided by 4.245 (diameter of the cylinder). The wallthickness is then equal to 0.0566 inch. This is the wall thickness of acylinder of the assumed diameter which would eventually burst under thepressure of 800 p.s.i. if the flange were not in some way supported toprevent bursting. The cylinder wall, however, supports the flange andprevents bursting of the flange, and the flange is simply expanded outto fill the 0.005 inch clearance space and seal against the opposed wallof the cylinder. This occurs at pressures of 800 p.s.i. and greaterpressures.

The wall thickness is also such that the expansive forces caused by thepressure are nonetheless within the elastic limits of the material usedin the piston so that the flange expands when the pressure is appliedand then recedes towards its original diameter when the pressure forcesare removed, thus again providing a normal running clearance between theflange and the cylinder wall.

It should be understood that the foregoing is intended only as aspecific example of the manner in which the wall thickness of the flangecan be calculated. The foregoing calculations and assumptions may beused for any type of piston material, and any type of pressurized pistonand cylinder assembly in which the working pressures within thepressurized space of the cylinder can either be assumed or calculated.

While the flange expansion is formulated as indicated, this may beaccompanied by some incidental thermal expansion of the flanges due toincreased temperatures of the flanges. The cylinder may also expand withtemperature. Effects of temperature are to be neglected when forming theflanges as set forth herein. It is not intended that the invention beused with high operating temperatures as are found in the cylinders ofinternal combustion engines during the time that a fuel mixture explodeswithin the cylinder. Temperatures within the cylinders using theinvention may vary considerably and still be well below that found inthe cylinders of internal combustion engines.

While the wall thickness may thus be calculated, it is usuallyadvantageous to utilize a somewhat lesser wall thickness. In thisregard, the presence of oil entrapping grooves lessens the effectivewall thickness to some extent. The wall thickness may, for example, withthe assumed values of piston diameter and cylinder diameter, be reducedto 0.026 inch (without a reduction by the grooves).

The interior corners of the flanges may be given a slight radius asindicated at 16 and 17.

When pistons are formed, as disclosed herein, and with the skirt-likeflange opposed to the pressurized space within the cylinder, theskirt-like flange bulges outwardly as schematically indicated in FIG. 3.In FIG. 3 the amount of expansion and the clearance space between thepiston and cylinder is exaggerated for purposes of illustration. It maybe noted that the skirt tends to assume a more or less barrel shape withthe heaviest contact occurring at areas intermediate the ends of theskit-t as indicated at 18. Wear masks on a piston formed with thechatacteristic skirt-like flanges will appear as indicated schematicallyin FIG. 4. The heaviest wear marks will appear in the regions designated19 which are areas intermediate the ends of the skirt-like flanges andlighter scratch marks will appear at the ends of the skirt-like flangeas indicated at 20. Relatively light scratch or wear marks will appearon the piston intermediate of the skirt-like flanges as indicated at 21.

It is important that the skirt-like flanges have shapes such that theymay expand in more or less barrel-like fashion. From a machining coststandpoint, a flange of essentially uniform wall thickness may be mostdesirable. The flanges may, however, have reduced thicknesses at theirouter end portions toprovide a stepped configuration. Such a reducedthickness is indicated at 22 in FIG. 5. FIG. 5 again shows anexaggerated clearance space between the piston and cylinder and anexaggerated expansion of the skirt-like flange to illustrate theprinciple involved. When the outermost portion of the skirt-like flangeis given a stepped configuration as indicated in FIG. 5, the skirt-likeflange has a relatively heavier sealing contact at the outer areas ofthe flanges than is indicated at 20 in FIG. 4 without the steppedconfiguration. The stepped configuration thusprovides a relativelylarger area of sealing contact with the opposed cylinder wall.

The skirt-like flanges may have other shapes. FIGS. 6, 7, 8 and 9illustrate other shapes which may produce the characteristic sealingengagement. In FIG. 6, for example, the skirt-like flange 23 has thesame calculable thickness as desribed. The flange, however, has anintumed lip 24 at the outer end thereof which tends to strengthen theouter end portion of the skirt-like flange and produce a more pronouncedoutward expanding effect in the medial portion of the skirt-like flangeto produce sealing action in the medial area of the flange.

In FIG. 7 the inner surface of the skirt-like flange 25 is rounded so asto produce regions of greatest thickness at the outer end of the flangeas at 26 and at the inner end of the flange as at 27. The effect again,as in the structure of FIG. 7, is to increase the outward expandingtendency in the medial portion of the skirt-like flange.

In FIG. 8 the inner surface of the skirt-like flange 28 is given acurvature opposite to that illustrated in FIG. 6. This tends to reducethe outward expansion in the medial portion of the flange and increasethe outward expansion at the outer end of the skirt-like flange as at29.

In FIG. 9 the skirt-like flange 30 has an expanding width from the innerportion 31 thereof to the outer end 32 thereof. Again, the configurationin FIG. 9 is such as to produce the greatest amount of expansion in themedial region of the skirt-like flange with lesser amounts of expansionand sealing contact at the outer end of the flange.

In FIG. the skirt-like flange 33 is tapered so that the width thereofdiminishes toward the outer end 34 of the skirt-like flange.

It should be understood that the variant forms of skirt-like flangesillustrated in FIGS. 6-10 are exaggerated in terms of variantthicknesses somewhat. These figures are intended to demonstrate thatsome variation from a uniform or substantially uniform wall thickness ispossible in the skirt-like flanges while at the same time producing theouter bulging effect and the areato-area sealing contact in medialportions of the skirtlike flanges. For example, if the degree of taperof the skirt-like flange 33 in FIG 10 is great enough, outward bulgingof the complete flange does not take place, although some outwarddeflection of the flange may take place so that the outermost comer ofthe skirt-like flange makes essentially a line contact with the cylinderwall as opposed to the outward bulging effect and relatively large areaof contact produced through the principles of the present invention.

In all forms of the invention, the wall thickness of the skirt-likeflanges is calculated so as to expand outwardly and make sealing contactwith the cylinder wall at pressures below the normal working pressures.This provides good sealing of the piston and cylinder without the needfor piston rings. At the same time, the pistons are formed so that theyhave a normal running clearance with the cylinder wall in theunpressurized condition. This facilitates assembly and reduces costs.The outward bulging of the flanges, as defined herein, is to bedistinguished from a simple bending movement of a flange which may occurby reason of a more or less pivotal movement about the main juncture ofthe flange and main body of the piston, in the case of flanges notcalculated as herein described.

I claim:

1. A piston and cylinder assembly of the type wherein a piston isreciprocally mounted within a cylinder to produce variant pressureconditions on opposite sides of the piston during reciprocation thereof,the improvement comprising a cylinder and a piston reciprocally mountedtherein, to develop a pressurized space in said cylinder, said pistonhaving an outside wall surface providing .a normal running clearancewith the opposed wall of said cylinder and with a clearance spacebetween the piston wall surface and the opposed cylinder wall, saidpiston having an extended skirt-like flange on the end thereof opposedto a closed end of the cylinder, said flange having a continuouscircular wall, the normal outside diameter of said skirt-like flangebeing such as to provide a normal running clearance with a space betweenthe wall of the flange and the opposed wall of the cylinder when thepiston is positioned within the cylinder in an unpressurized condition,said skirt-like flange having a radial width and an axial length such,with relation to the outside diameter of said. piston and flange, withrelation to the particular material of which the piston and skirt-likeflange are made, and with relation to the normal operating pressuredeveloped within the cylinder against the end of the piston carryingsaid skirt-like flange, that said skirt-like flange is expandedoutwardly because of the hoop-like bursting stresses developed thereinduring normal operating pressures such that the outer wall of saidskirt-like flange is forced into wiping and sealing contact with theopposed wall of the cylinder during reciprocation of said piston, saidpistonand cylinder being further characterized by the absence of sealingrings or expansion rings, the wall thickness of said flange being suchthat the stresses developed on said flange are within the elastic limitsof the material of the flange whereby the flange resiliently recedestoward its original condition after removal of said pressurizedcondition.

2. The structure of claim 1 wherein the thickness and length of theflanges are such, with relation to the specific material of the pistonand flange and with respect to the normal operating pressures of theassembly, that the wiping and sealing pressure exerted by said skirtlikeflange on the opposed wall of said cylinder is greatest at the areasintermediate the ends of said flange.

3. The structure of claim 1 wherein the wall thickness of said flange iscalculated to be that wall thickness which will expand and burst at apressure below the normal operating pressure of the piston and cylinderterior wall thereof. l I

1. A piston and cylinder assembly of the type wherein a piston isreciprocally mounted within a cylinder to produce variant pressureconditions on opposite sides of the piston during reciprocation thereof,the improvement comprising a cylinder and a piston reciprocally mountedtherein, to develop a pressurized space in said cylinder, said pistonhaving an outside wall surfAce providing a normal running clearance withthe opposed wall of said cylinder and with a clearance space between thepiston wall surface and the opposed cylinder wall, said piston having anextended skirt-like flange on the end thereof opposed to a closed end ofthe cylinder, said flange having a continuous circular wall, the normaloutside diameter of said skirt-like flange being such as to provide anormal running clearance with a space between the wall of the flange andthe opposed wall of the cylinder when the piston is positioned withinthe cylinder in an unpressurized condition, said skirt-like flangehaving a radial width and an axial length such, with relation to theoutside diameter of said piston and flange, with relation to theparticular material of which the piston and skirt-like flange are made,and with relation to the normal operating pressure developed within thecylinder against the end of the piston carrying said skirt-like flange,that said skirt-like flange is expanded outwardly because of thehoop-like bursting stresses developed therein during normal operatingpressures such that the outer wall of said skirt-like flange is forcedinto wiping and sealing contact with the opposed wall of the cylinderduring reciprocation of said piston, said piston and cylinder beingfurther characterized by the absence of sealing rings or expansionrings, the wall thickness of said flange being such that the stressesdeveloped on said flange are within the elastic limits of the materialof the flange whereby the flange resiliently recedes toward its originalcondition after removal of said pressurized condition.
 2. The structureof claim 1 wherein the thickness and length of the flanges are such,with relation to the specific material of the piston and flange and withrespect to the normal operating pressures of the assembly, that thewiping and sealing pressure exerted by said skirt-like flange on theopposed wall of said cylinder is greatest at the areas intermediate theends of said flange.
 3. The structure of claim 1 wherein the wallthickness of said flange is calculated to be that wall thickness whichwill expand and burst at a pressure below the normal operating pressureof the piston and cylinder assembly unless the flange is supported. 4.The structure of claim 1 wherein the length of the flange isapproximately equal to one-quarter of the piston external diameter. 5.The structure of claim 1 wherein said piston has a similarly formedflange, as previously defined, on each end of said piston.
 6. Thestructure of claim 5 wherein each said flange has at least one oilentrapping groove formed in the exterior wall thereof.